1. Field of the Invention
The present invention relates to a CAD (Computer Aided Design) system, a method of producing a three-dimensional model using the CAD system, and a storage media which stores programs for producing a three-dimensional model.
2. Description of Related Art
Japanese Patent Application Publication (Kokai) No.7-249133 describes a three-dimensional CAD system for forming a stereoscopic model for an specific article for which many kinds of variations exist.
According to the above referenced patent publication, a shape model of a three-dimensional article is produced with a system having a unit for dividing a similarly configured article into a plurality of representative portions, a unit for classifying partial shapes into qualitative shapes, a database for standardizing and registering the classified qualitative shapes, and a unit for defining dimensional relationship of the classified qualitative shapes in terms of parameters and for assigning dimensions.
The above identified patent publication discloses a method of producing a three-dimensional model of a new conrod by dividing a conrod 400 as shown in FIG. 22 into three parts, a larger end part 401, a neck 402, and a smaller end part 403, providing ten-odd kinds of qualitative shapes to each part, and inputting values of relative dimensions defined as parameters of these qualitative shapes.
Parametric designing is also described in Japanese Patent Application Publication (Kokai) Nos. 7-254075 and 7-296039.
In the prior art, when there are registered qualitative shapes, any partial shapes can be obtained by inputting values of relative dimensions in terms of parameters, and three-dimensional models are obtained by combining the partial shapes. As regards the shapes which are not registered, however, all of shapes must be input and then registered into a database to generate a three-dimensional model. As such, it is not easy to form a three-dimensional model other than by using old shapes to create similar shapes.
Further, as to difference of the shapes of minute portions of a stored shape, if a first curved line of included in the shape data is modified, other curved lines which intersect the first curved line as well as curved surfaces whose boundary lines include the first curved line need to be modified, which is cumbersome.